I am also starting to feel that our community blogs do not work well for communication.

I think that this is more than renaming and we cannot change anything before we have some prototypes that can be discussed. I will add it to my longlonglong todo list.

One thing that developers can find out now - is there some Plone forum software that can be used, or should we develop our own forum? I think it is better to use some existing forum, but it should be extremely simple.

Plone has a built-in commenting functionality that is extremely simple. Any content object can be commented if commenting is enabled from its properties. Comments can be replies to other comments, so basically you get a bunch of message threads after the usual content of the object.

If that's not good enough, then we jump from simplicity to functionality with something like TIForum, which I guess is currently the best forum for Plone.